1. Field of the Invention
The present invention relates generally to power supplies and, more specifically, the present invention relates to a switched mode power supply controller.
2. Background Information
Electronic devices use power to operate. Switched mode power supplies are commonly used due to their high efficiency and good output regulation to power many of today's electronic devices. In a known switched mode power supply, a low frequency (e.g. 50 Hz or 60 Hz mains frequency), high voltage alternating current (AC) is converted to high voltage direct current (DC) with a diode rectifier and capacitor. The high voltage DC is then converted to high frequency (e.g. 30 to 300 kHz) AC, using a switched mode power supply control circuit. This high frequency, high voltage AC is applied to a transformer to transform the voltage, usually to a lower voltage, and to provide safety isolation. The output of the transformer is rectified to provide a regulated DC output, which may be used to power an electronic device. The switched mode power supply control circuit provides usually output regulation by sensing the output controlling it in a closed loop.
A switched mode power supply may include an integrated circuit power supply controller coupled in series with a primary winding of the transformer. Energy is transferred to a secondary winding from the primary winding in a manner controlled by the power supply controller to provide the clean and steady source of power at the DC output. The transformer of a switched mode power supply may also include another winding called a bias or feedback winding. The bias winding provides the operating power for the power supply controller and in some cases it also provides a feedback or control signal to the power supply controller. In some switched mode power supplies, the feedback or control signal can come through an opto-coupler from a sense circuit coupled to the DC output. The feedback or control signal may be used to modulate a duty cycle of a switching waveform generated by the power supply controller or may be used to disable some of the cycles of the switching waveform generated by the power supply controller to control the DC output voltage.
A power supply designer may desire to configure the power supply controller of a switched mode power supply in a variety of different ways, depending on for example the particular application and/or operating conditions. For instance, there may be one application in which the power supply designer would like the power supply controller to have one particular functionality and there may be another application in which the power supply designer would like the power supply controller to have another particular functionality. It would be convenient for power supply designer to be able to use the same integrated power supply controller for these different functions.
In order to provide the specific functions to the power supply controller, additional pins or electrical terminals are added for each function to the integrated circuit power supply controllers. Consequently, each additional function generally translates into an additional pin on the power supply controller chip, which translates into increased costs and additional external components. Another consequence of providing additional functionality to power supply controllers is that there is sometimes a substantial increase in power consumption by providing the additional functionality.